1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine for controlling to correct an influence of a fuel property, and more particularly, to a control apparatus for an internal combustion engine to calculate the fuel property based on an actual combustion state without using a property sensor, so as to suppress a deterioration of an exhaust gas and to enhance a drivability by correcting a control parameter in accordance with the fuel property.
2. Description of the Related Art
FIG. 22 schematically shows a structure of a conventional control apparatus for an internal combustion engine. In FIG. 22, the internal combustion engine, i.e., an engine 1 discharges an exhaust gas by burning an intake air (mixed gas) in which a fuel is ejected.
A suction pipe 2 connected to an intake side of the engine 1 takes in an air in the atmosphere and supplies the air to the engine 1. An air cleaner 2a mounted to a suction port of the suction pipe 2 removes rubbishes and dusts in the atmosphere for cleaning the intake air to the engine 1. An air flow sensor 31 provided in the suction pipe 2 detects an amount of intake air (intake amount) Qa.
A throttle valve 4 provided in the suction pipe 2 interlockingly operates with an accelerator pedal (not shown) such as to adjust a passage area and control the amount of intake air which passes through the suction pipe 2.
An intake manifold 5 provided at downstream of the suction pipe 2 uniformly supplies the air inhaled through the throttle valve 4 to each of cylinders of the engine 1.
An exhaust pipe 6 connected to an exhaust side of the engine 1 discharges an exhaust gas generated after the combustion in the engine 1. A catalyst 7 provided in the exhaust pipe 6 purifies the exhaust gas by a chemical reaction and discharges the same into the atmosphere.
A throttle opening degree sensor 8 provided in the throttle valve 4 detects a throttle opening degree .theta.. A crank angle sensor 9 provided on a crankshaft of the engine 1 generates a crank angle signal SGT which indicates a crank angle reference position for each of the cylinders.
A camshaft which synchronously rotates with the crankshaft at a rotational ratio of 1:2 is provided with a known cylinder identify sensor (not shown) which generates a cylinder identify signal.
An injector 10 provided in the intake manifold 5 ejects a fuel into the intake air which is just before inhaled into the engine 1, and mixes into the mixed gas.
An air-fuel ratio sensor 11 provided in the exhaust pipe 6 detects a density of oxygen contained in the exhaust gas for generating an air-fuel ratio information F.
The air flow sensor 3, the throttle opening degree sensor 8, the crank angle sensor 9 and the air-fuel ratio sensor 11 constitute various sensors for detecting the driving state of the engine 1.
The intake amount Qa, the throttle opening degree .theta., the crank angle signal SGT and the air-fuel ratio information F are detected information which indicates the operation state. The crank angle signal SGT is also used as a signal which indicates the number or revolutions of the engine 1.
An ECU (electric controlling unit) 12 comprising a microcomputer calculates a control parameter of the engine 1 based on the detected information Qa, .theta., SGT and F from the various sensors 3, 8, 9 and 11, and outputs control signals J and P with respect to various actuators such as an injector 10 and an ignition apparatus 20.
The ignition apparatus 20 including an ignition coil and an igniter applies a high voltage to an ignition plug (not shown) in each of the cylinders of the engine 1.
The injector 10 is driven by the fuel injection signal J from the ECU 12, and the ignition apparatus 20 is driven by the ignition signal P from the ECU 12.
Although it is not shown in the drawings here, for detecting the driving state, there are provided various sensors such as a water temperature sensor for detecting a cooling water temperature of the engine 1, and pressure sensor for detecting pressure in the intake manifold 5 and cylinders.
Further, there are provided, as various actuators, a bypass valve and an EGR valve for controlling the intake amount at the time of idling.
FIG. 23 is a block diagram showing a detailed structure of the ECU 12 as shown in FIG. 22. In FIG. 23, a battery 13 mounted in the automobile functions as a power source for ECU 12 and various apparatuses mounted in the automobile.
An ignition key switch 14 inserted in an output terminal of the battery 13 closes when the engine 1 is actuated, and supplies an electric power output from the battery 13 to the ECU 12 and various apparatuses mounted in the automobile.
The ECU 12 takes in a detected driving state information (i.e., crank angle signal SGT, the intake amount Qa, the air-fuel ratio information F and the throttle opening degree .theta.) from the various sensors, and calculates control parameters such as a fuel injection amount and a timing of ignition in accordance with these detected information, and outputs a fuel injection signal J to the injector 10 and the ignition signal P to the ignition apparatus 20.
The ECU 12 includes a microcomputer 100, input interface circuits (which will be referred to as input I/F) 101 to 103, an output interface circuit (which will be referred to as output I/F) and a power source circuit 105.
The microcomputer 100 constitutes control calculating means for calculating a control parameter. The input I/F 101 to 103 take in the detected information from the various sensors, and input them to the microcomputer 100. The output I/F 104 outputs the control signals J and P calculated in the microcomputer 100.
The power source circuit 105 is connected to the battery 14 through the ignition key switch 14.
The microcomputer 100 in the ECU 12 includes a CPU 200, a counter 201, a timer 202, an A/D converter 203, an input port 204, a RAM 205, a ROM 206, an output port 207 and a common bus 208. These elements 201 to 207 are connected to the CPU 200 through the common bus 208.
The CPU 200 calculates control parameters (such as control signals J and P) based on the detected information SGT, Qa, F and .theta. in accordance with a predetermined program in the ROM 206.
The free-running counter 201 counts various control times for measuring a rotational cycle of the engine 1.
The A/D converter 203 converts an analogue input signal via the input I/F 102 into a digital signal and inputs the same to the CPU 200.
The RAM 205 is used as a work memory when the CPU 200 calculates. Various operation programs are stored in ROM 206. The output port 207 outputs the control signals J and P or the like.
Each of the input I/F changes a wave form of the crank angle single SGT into in interrupt signal and inputs the same to the microcomputer 100. In replying to the interrupt signal, the CPU 200 in the microcomputer 100 reads a value of the counter 201, and calculates the rotational cycle of the engine 1 based on a difference between the current read value and the last time read value, and store the result in the RAM 205.
The input I/F 102 reads each of the detected information Qa, F and .theta., and inputs them to the A/D converter 203 in the microcomputer 100.
The input I/F 103 reads other detected information, and inputs them to the input port 204 in the microcomputer 100.
The input I/F 104 amplifies the control signals J and P from the output port 207 and the like, and outputs them to the injector 10 and the ignition apparatus 20.
With reference to FIGS. 24 and 25, the operation for controlling the fuel injection amount by the conventional control apparatus for the internal combustion engine as shown in FIGS. 22 and 23 will be described. The description is made based on a case in which an air-fuel ratio feedback control is conducted.
FIG. 24 is a block diagram showing a functional structure of fuel injection amount calculating means 12F in the ECU 12. FIG. 25 is a wave form chart showing the operation of the fuel injection amount calculating means 12F based on the air-fuel ratio information F, and shows variations in the air-fuel ratio information F and a normal fuel injection signal CF as time passes.
In FIG. 24, the fuel injection amount calculating means 12F includes a PI controller 400, various calculators 401 to 405, and producing means 501 to 505 for producing various data values.
Further, as the occasion demands, an adder-subtracter 406 and acceleration/deceleration correction amount producing means 506 are provided.
The predetermined air-fuel ratio producing means 501 produces a predetermined air-fuel ratio Fr which is a target value. The basic fuel amount producing means 502 produces a basic fuel amount Fo to be injected from the injector 10 based on the intake amount Qa. The fuel correction amount producing means 503 produces a fuel correction amount Fc based on a warm-up state of the engine 1, enrich coefficient and the like.
The acceleration/deceleration correction amount producing means 506 produces an acceleration/deceleration correction amount Fca in accordance with an acceleration/deceleration state based on the throttle opening degree .theta. and the like.
The correction coefficient producing means 504 produces a correction coefficient KF for converting the fuel injection amount into a driving time of the injector 10. A useless time producing means 505 produces a useless time TF when the injector starts driving.
The substracter 401 calculates an air-fuel ratio deviation .DELTA.F between a predetermined air-fuel ratio Fr and the air-fuel ratio information F. The PI controller calculates the correction amount CF by the air-fuel ratio feedback control based on the air-fuel ratio deviation .DELTA.F, and when the air-fuel ratio sensor 11 is inactivated, the correction amount CF is set at 1.0.
The multiplier 402 multiplies the correction amount CF by a basic fuel amount Fo, and the multiplied result is input to the multiplier 403. The multiplier 403 multiplies the multiplied result of the multiplier 402 by the fuel correction amount Fc, and such multiplied result is input to the multiplier 404. The multiplier 404 multiplies the multiplied result of the multiplier 403 by the correction coefficient KF, and such multiplied result is input to the multiplier 405.
When the acceleration/deceleration correction is conducted, the adder-subtracter 406 adds or subtracts the acceleration/deceleration correction amount Fca to or from the multiplied result of the multiplier 403, and such calculated result is input to the multiplier 404.
The adder-subtracter 405 adds the useless time TF to the multiplied result of the multiplier 404, and the added result is output to the injector 10 as the fuel injection signal J.
At that time, the PI controller 400 which conducts the air-fuel ratio correction based on the PI control produces a correction amount based on the feedback control as shown in FIG. 25, and determines variation amounts JLR and JRL of the correction amount CF such that the air-fuel ratio becomes a theoretical air-fuel ratio (14.7) even if the air-fuel ratio information F is changed from lean to rich, or from rich to lean.
When a linear output type oxygen concentration sensor is used as the air-fuel ratio sensor 11, the air-fuel ratio target value may be changed.
The correction amount CF produced by the PI controller 400 corresponds to a normal fuel injection signal.
In the meantime, the property (composition) of a fuel injected to the engine 1 is varies depending upon a location or season in which the fuel is used, and also varies depending upon a maker. In generally, a fuel property includes a light-duty type and a heavy-duty type, and there is a fear that an inconvenient driving problem may be generated due to a difference in the fuel property.
In order to prevent such an inconvenient driving problem due to the difference in the fuel property from being generated, it is conceived that the fuel injection amount should be set higher such that the air-fuel ratio tends to be rich. However, this measure causes a problem that the fuel efficiency is deteriorated and it is not economical.
On the other hand, paying attention to the fact that there is an interrelation between the fuel property and an alcohol concentration, there is conventionally proposed a control apparatus for detecting the fuel property using an alcohol concentration sensor.
For example, in a control apparatus for an internal combustion engine described in Japanese Utility Model Registration Publication No.6-611, the control amount is corrected in accordance with the fuel property detected by an alcohol concentration sensor, thereby overcoming the problem due to the difference in fuel property.
As described above, the conventional control apparatus for an internal combustion engine has problems that if the air-fuel ratio is enriched to prevent the problem due to the difference in fuel property, the fuel efficiency is deteriorated, and if the fuel property is detected using the alcohol concentration sensor to correct the control amount, a special sensor is required and the costs are increased.